Synthesis of New Tricyclic Phosphines and Phosphinites by Intramolecular Diels−Alder Reactions of Trivalent Phospholes

Phospholes bearing an allyl-X substituent at phosphorus tend to undergo an intramolecular Diels−Alder cycloaddition (IMDA) leading to the corresponding tricyclic derivative. When X = O or NR, the IMDA easily takes place at room temperature. When X = CH₂, the IMDA slowly takes place around 110−140 °C, as a function to the substitution pattern of the dienic system. Two tricyclic derivatives (X = O and CH₂) have been characterized by X-ray crystal structure analysis of the P-sulfides.